The invention relates to an encryption communication system, including a communication relay device that connects a first network and a second network, for encrypting a communication within the first network and a communication within the second network in a network system configured so that communications are performed between a client in the first network and a server in the second network via the communication relay device.
A VPN (Virtual Private Network) technology capable of encrypting authentication/data communications is employed as a technology, a so-called remote accessing technology, for a client existing in a remote area to perform communications with a host/server within the Intranet via the Internet.
The VPN provides a structure (framework) by which the client existing in the remote area can communicate directly with the host/server in the Intranet. A general type of remote access actualizing method is that a VPN gateway device is installed at a connection point between the Internet and the Intranet, and a virtual line (VPN tunnel) is generated between the client and the VPN gateway (see FIG. 10).
A VPN configuration technology for effecting such encryption is exemplified by IPSec (Internet Protocol Security: Security Architecture for Internet Protocol), SSL-VPN (Secure Socket Layer VPN) and so on.
In the case of establishing a connection between the remote areas by the VPN tunnel via the Internet, there might be a possibility of suffering attacks such as eavesdropping, falsification, posing (spoofing) and so on by ill-intentioned people because of via the public network. A frame sent across within the Internet is required to be invariably encrypted for safeguarding traffic from these attacks irrespective of whether authentication communication or data communication.
For encrypting the traffic in the VPN tunnel, the VPN gateway device and the client have a function of generating (establishing) an encryption session, and encrypting and decrypting the traffic passing through the session.
Namely, an encryption-side device converts data of the frame to be transmitted into a bit string impossible of being decrypted, while a decryption-side device decodes the data back to the bit string possible of being decrypted. The bit string used as a rule for converting the frame data is called a [key].
The encryption VPN communications using the key can be roughly categorized into two phases. These phases are an authentication phase and a data communication phase. In the authentication phase, there are executed processes of making authentication, determining the key utilized in the data communication phase and so on. In the data communication phase, there are executed processes of transmitting and receiving the encrypted frame by use of the key determined in the authentication phase, and so forth.
If holding the [key], it is possible to decrypt the encrypted communication in the data communication phase, and hence it is an indispensable condition for the encryption VPN technology to prevent the [key] from being leaked out to terminals other than the frame transmitting/receiving host.
A technology such as a public key encryption method, etc is given as a method of sharing the common key with between the client and the VPN gateway in a way that meets the condition described above.
The public key encryption method is an encryption method capable of preventing the key from being decrypted by preparing two types of keys such as an encryption key and a decryption key and making the encryption key open to the public (a public key) while retaining the decryption key without being opened (a secret key).
There is a common key encryption method different from the public key encryption method, wherein a key usable for both of the encryption process and the decryption process is prepared. The common key encryption method is an encryption method of exchanging the key information between two hosts performing the communications and sharing the same key (a common key) with each other.
The public key encryption method has a heavier load of the encryption/decryption processes than the common key encryption method, and therefore the common key encryption method is utilized in the data communication phase requiring a large number of encryption/decryption processes. Key exchange algorithms in the respective methods are described in a variety of documents (refer to, e.g., Non-Patent documents 1 and 2). The invention relates to an authentication/data communication encryption technology in the VPN described above.
Note that the VPN utilizing method includes, other than [the remote access VPN], a utilizing mode called a [base-to-base VPN], wherein a plurality of networks, which are physically apart from each other, are made to appear as if one single network (see FIG. 11).
The following discussion will proceed on the premise of the [remote access VPN], however, the application of the invention in the [base-to-base VPN] is not restricted.
At the present time, computerization in organizations such as business enterprises, public offices, etc gains a progress, and there increase the organizations in which information such as customer individual information, etc accessible by only some members within the organizations are stored on servers in the Intranets.
Accordingly, the mere VPN-based encryption within the Intranet is insufficient as a countermeasure in security, and the traffic inside the Intranet needs encrypting, thereby necessitating the information to be protected from the malicious attacks.
As explained above, in the case of actualizing the encryption both in the Intranet and in the Internet, any one of the following types of encryption is to be conducted in addition to the encryption of the session between the VPN gateway and the client.
In the case of a prior art 1 (see FIG. 12A and FIG. 12B), in the authentication phase, the encryption sessions are generated (established) between the client and the VPN gateway and between the VPN gateway and the server, respectively. In the data communication phase, the VPN gateway, when receiving the frame from the client, decrypts the frame once with a client-side common key, then encrypts the frame with a server-side common key, and transmits the encrypted frame to the server. The VPN gateway, when receiving the frame from the server, decrypts the frame with the server-side common key, then encrypts the frame with the client-side common key, and transmits the encrypted frame to the client.
In the case of a prior art 2 (see FIG. 13A and FIG. 13B), in the authentication phase, the encryption sessions are generated between the client and the VPN gateway and between the client and the server, respectively. In the data communication phase, the VPN gateway, when receiving the frame from the client, decrypts the frame with the client-side common key and sends the frame to the server. The VPN gateway, when receiving the frame from the server, encrypts the frame with the client-side common key and sends the frame to the client.
Thus, the VPN gateway in each of the prior arts 1 and 2 requires the processes of encrypting and decrypting all the frames passing through in the data communication phase.
The VPN gateway resides at a boundary between the Internet and the Intranet and is therefore in an easy-to-concentrate position of the traffic.
Further, it is considered that a much greater amount of traffic passes through the VPN gateway from now onward because of an increase in quantity of information (data size) that can be processed by a single host owing to client/server enhanced performance and a rise in the number of users who utilize the Internet.
The encryption/decryption process essentially involves a great calculated amount and is one of processes that consume a large quantity of CPU resources. As described above, the VPN gateway executes this kind of encryption/decryption processes for all the frames passing through the VPN gateway.
Accordingly, if the traffic concentrates at the VPN gateway, there arises a problem that the encryption/decryption process by the VPN gateway turns out a bottleneck in end/host communications.
Note that the following is what is considered to be related to the invention (refer to Non-Patent documents 1 and 2).
[Non-Patent document 1]
“Mastering IPSec”, authored By Tatuya Baba, published by Orly Japan
[Non-Patent document 2]